A. Field of the Invention
The present invention relates to a medical tube having a shape memory alloy and, more particularly, to a medical tube used in, e.g., an insertion portion of an endoscope and inserted in a body cavity.
B. Description of the Prior Art
A conventional medical tube having a shape memory alloy is disclosed in Japanese Utility Model Disclosure (Kokai) No. 59-2344. This medical tube comprises a plurality of shape memory alloys in the form of wires having a transformation temperature of 30.degree. C. to 60.degree. C. A power source is connected to these shape memory alloys. The shape memory alloys are energized, heated, and deformed in a predetermined direction, thereby bending the tube as a whole.
The medical tube is used while inserted in a living organism. Before the tube is used, it must be sterilized and disinfected. More specifically, the tube is usually placed in a sterilizer and sterilized using an ethylene oxide gas.
However, the temperature of the sterilizer often exceeds a transformation temperature of a shape memory alloy embedded in the tube. For this reason, the shape memory alloy in the tube tends to restore the memorized shape while it is being held in a predetermined shape in the sterilizer. Especially in a tube having a plurality of wire memory alloys, all the alloys tend to restore the memorized shapes simultaneously. As a result, the restoration force of the shape memory alloy is weakened. In other words, the shape memory alloy cannot satisfactorily restore the memorized shape. The main body of the medical tube may be damaged since the shape memory alloy tends to restore its memorized shape while being held in the predetermined position.
During aeration for eliminating the residual gas in the sterilizer after the tube is sterilized, heat having a temperature exceeding the transformation temperature of the shape memory alloy is applied to the tube. As a result, the same problem posed by sterilization occurs.